The present invention relates to the art of electric arc welding of the type where a welding wire is directed toward a workpiece and an electrical current is passed through the welding wire to the workpiece to create an arc welding process melting the end of the advancing wire and depositing the melted metal onto the workpiece and more particularly to an improved welding wire for use in this arc welding process and the method of making this improved welding wire.
Electric arc welding of the type to which the present invention is directed involves the use of a welding wire normally stored upon a spool or reel, which wire is fed from the supply reel toward a workpiece through a tubular connector so that current can be directed through the connector to the advancing welding wire and through the welding wire to the workpiece. The electric current heats the advancing welding wire by I2R heating so that the end of the welding wire is melted and deposited onto the workpiece by transfer through the arc or by other electrical and mechanical phenomenon. Thus, the advancing wire conducts the welding current which melts the wire for deposition of the molten metal from the end of the wire onto the workpiece. Through the years there have been substantial improvements in the welding wire, which is normally a solid wire having a predetermined diameter and a surface lubricant so the wire can be advanced at a controlled feed speed for melting and depositing the molten metal onto the workpiece. Shielding gas can be used around the advancing welding wire. A solid wire provides superior arc welding properties; however, it is often necessary to provide the welding wire with flux and alloying metal ingredients to tailor the molten metal deposition to the desired metallurgical demands of the welding process. To accomplish these added features, it has become common practice to form the wire as a steel sheath surrounding a center core formed from fluxing ingredients and/or alloying powder. Thus, there are many cored welding wires. By using a cored wire concept, the flux can be evenly distributed along the length of the advancing welding wire. When producing the metal sheath from a somewhat standard steel, the core can include alloying powder. These metal cored electrodes employ the powdered metal in the core to tailor the deposited metal for a given welding process. There is a substantial advantage in some welding processes to use the flux cored or metal cored wire. Indeed, there are instances when a combination flux and alloy powder are used in the core of the wire. The advantages of these cored wires or electrodes for arc welding wire are somewhat offset by the fact that a solid metal wire normally produces superior arc welding. The metal is at the center of the arc and in a sheath surrounding the arc, as in a flux cored or metal cored wire. Both a solid metal wire and a metal cored wire have a substantially constant resistance per length of wire, which resistance controls the arc welding process especially in constant voltage arc welding procedures. In some arc welding processes, it is desirable to have an increased resistance per length to optimize the welding process, but such a modification affects the amount of metal being deposited. The solid metal wire and the cored metal wire satisfy the demands of the electric arc welding industry; however, they have disadvantages caused by the constraints of their physical characteristics which in some instances does not allow optimum electrical characteristics of the welding process.
The present invention is a solid metal welding wire which has distinct quantized segments that facilitate superior droplet transfer. The segments each have essentially the same volume. This use of a solid welding wire with quantized distinct segments separated by bridging elements has been found to perform well with conventional constant voltage welding sources. The current or heating is controlled by the effective resistance or resistance per length, which resistance is increased by using interconnecting smaller bridging elements between the larger segments. This type of solid wire has the advantage that it is easily made by simply processing existing solid MIG wire in a manner to produce a series of spaced indentations creating a quantized segment between adjacent indentations. Such indentations can be done at the manufacturing facility making the solid wire or in a device adjacent to the wire feeder at the welding station, which is often a robotic welding station. By using quantized spaced segments in a solid welding wire, pulsed arc welding can be coordinated so that the pulse frequency and the wire feed rate provide a quantized segment at the time of each current pulse. This coordination stabilizes the pulsed mode transfer so that a single droplet detachment is achieved with each current pulse to optimize the welding characteristics in ways well known in the welding art. The electrode is heated by current passing through the wire. The resistance of the wire has a direct effect on the heating. Thus, by using smaller areas between the quantized segments, the effective resistance or resistance per length is increased and the current is decreased when a constant voltage is applied to the welding process. This adjustment of resistance controls the heating of the advancing welding wire in a manner determined by the area and length of the bridging elements created by the indentations defining the spaced quantized segments. By using the present invention, the resistance per length of wire is higher than with a solid wire with the same outer diameter. This is an advantage at high deposition rates because the heat input into the workpiece per unit weight of wire can be reduced to extend the stable range of the constant voltage process. By reducing the cross sectional area of the metal in the bridging element between the quantized segments, the resistance per length can be modified in a tailored fashion. The shape of the indentations creating the bridging elements between the quantized segments of the solid wire electrode can be in the form of circular grooves or other configurations which reduce the area and, thus, increase the resistance of the solid wire between the quantized segments. If the bridging elements are in the form of circular grooves, the solid metal wire can be provided with fluxing, filling or alloying agents, such that the agents are carried by the grooves without affecting the outer diameter of the metal wire. Electrical contact is maintained at the outer portions of the quantized segments. By adjusting the relative length of the quantized segments and the length of the groove forming the connecting elements, the desired amount of fluxing or alloying agents can be provided per length of the advancing solid metal welding wire. Such solid wire has the advantages of standard solid wire with the added advantage of a flux cored or metal cored wire. To protect the fluxing, filling or alloying agents in the space created by the indentations forming the bridging elements, another aspect of the invention includes the use of a metal sheath around the metal electrode. This sheath can be steel or copper to enhance electrical conduction from the electrical contact in the welding equipment to the advancing solid metal welding wire. Thus, moisture contamination and physical damage to the fluxing, filling or alloying agents is inhibited. The sheath or jacket can be mechanically wrapped around the wire having spaced quantized segments by using a standard spiral wrapping technique. The sheath or jacket can be placed around the wire and drawn or rolled with the wire, using techniques similar to those employed in conventional cored wired manufacturing techniques. The sheath or jacket can also be provided by a plating technique or a plasma spray technique so long as the sheath or jacket around the quantized segments is electrically conductive. Indeed, such a sheath or jacket can be placed around the quantized segments forming the solid metal welding wire without the use of filling agents merely to enhance the electrical characteristics, or appearance, of the advancing metal wire stored on a spool for use in an automatic or semi-automatic electric arc welding process.
In accordance with the present invention, there is provided a welding wire for use in electric arc welding wherein the welding wire has an effective outer diameter and comprises a length of solid metal formed into a series of distinct segments, each having a selected volume and joined together by interconnecting bridging elements with the cross sectional area of the solid metal at these segments being greater than the cross sectional area of the solid metal at the bridging elements. In this manner, the solid metal welding wire has distinct quantized segments. By controlling the contour of the connecting bridging elements, the resistance per length of welding wire can be changed to control the welding process so that a lesser amount of current will be needed to deposit a given amount of molten metal.
In accordance with another aspect of the present invention, the bridging elements are formed by indentations, such as circular grooves, which indentations may be filled with a fluxing agent, alloying metal powder or other constituents to control the metallurgy and fluxing characteristics of the metal wire while maintaining the advantage of a solid metal arc welding wire.
In accordance with another aspect of the present invention, the quantized distinct metal segments have a maximum cross sectional area essentially defining the effective outer diameter of the solid metal welding wire while the bridging elements of the wire have a maximum cross sectional area that is substantially less than the maximum cross sectional area of the quantized segments.
In accordance with still a further aspect of the present invention, there is provided a method of producing a solid welding wire for electric arc welding, which method comprises the steps of conveying a solid metal welding wire along a given path and forming a series of indentations in the wire at equally spaced locations to define a series of distinct metal segments each having a selected volume. These quantized metal segments are joined together by bridging elements determined by the shape of the separating indentations. In practice, the indentations are circular grooves between the quantized metal segments of the solid welding wire.
In accordance with still a further aspect of the invention, this method includes the step of depositing granular flux into the indentations or depositing powder alloying metal into the indentations. In this manner, the indentations can control the even distribution of alloying agents and/or fluxing agents along the length of the solid welding wire, without requiring the use of a cored wire concept. The method also contemplates the further implementation of an aspect of the invention wherein a metal sheath of steel or other conductive material is placed around the solid metal welding wire.
By using the invention, the series of distinct quantized metal segments that are joined together by interconnecting bridging elements can have effective resistance of the solid metal welding wire accurately controlled by adjusting the relationship of the segments and bridging elements.
In accordance with another aspect of the present invention there is provided a method of controlling the resistance per length of a solid metal welding wire used for electric arc welding including the steps of providing a solid metal welding wire, forming a series of indentations in the wire at spaced locations whereby the resistance per length at the indentations is greater than the resistance per length of the wire between the indentations and controlling the size of the indentations to control the overall resistance per length of the wire. This method is further modified by including the step of controlling the spaces between the indentations to provide quantized segments of generally equal volume of metal.
The primary object of the present invention is the provision of a solid metal welding wire, which wire has a series of distinct, quantized segments joined together by bridging elements.
Another object of the present invention is the provision of a solid metal wire, as defined above, which solid metal wire can be produced from a standard MIG wire at the manufacturing facility or adjacent the wire feeding device in the welding area.
Yet another object of the present invention is the provision of a solid metal welding wire, as defined above, which wire has improved arc stability and controlled heat input. The wire can greatly facilitate pulse arc welding in a constant voltage welding process.
Still a further object of the present invention is the provision of a solid metal welding wire, as defined above, which wire can be produced to have a controlled resistance per length greater than the resistance per length of a metal wire of the same diameter.
A further object of the present invention is the provision of a solid metal welding wire, as defined above, which wire can be produced to control the resistance of the wire stick out per unit volume of wire directed to the workpiece.
Another object of the present invention is the provision of a solid metal welding wire, which wire has a greater resistance per length than a solid wire of the same diameter. This object is an advantage at very high deposition rates due to a reduced heat input to the workpiece per unit length of wire; thus extending the stable range of a constant voltage process.
Still a further object of the present invention is the provision of a solid metal welding wire, as defined above, which welding wire can have controlled resistance per unit length or controlled resistance of the stick out merely by utilizing a series of indentations defining the distinct quantized segments of the wire.
Another object of the present invention is the provision of a solid metal welding wire, as defined above, which welding wire can be coordinated with a pulse welding process so that a quantized segment of the wire is provided to the arc of the welding process simultaneously with each current pulse.
A further object of the present invention is the provision of a solid metal welding wire, as defined above, which welding wire can be provided with fluxing, filling and/or alloying agents that can be carried with the wire while maintaining the solid metal characteristics of the welding wire. In addition, the wire of the present invention can be provided with an outer metal sheath to hold the fluxing, filling or alloying agents and/or to increase the conductivity to the advancing metal welding wire during the welding process.
Another primary object of the present invention is the provision of a method of producing a welding wire for electric arc welding, which method forms a series of indentations in the wire to quantize segments of the wire so the wire can accept fluxing, filling and/or alloying agents and can have controlled resistance per length of wire.
Another object of the present invention is the provision of a method as defined above, which method can use a standard MIG welding wire and can be performed at a relatively low cost.